The present invention relates to an abnormality detecting device for an evaporative fuel processing system for processing evaporative fuel generated in a fuel tank containing fuel to be supplied to an internal combustion engine.
An abnormality detecting device for determining an abnormality in an evaporative fuel processing system is known from Japanese Patent No. 2857656, for example. In this conventional abnormality detecting device, a negative pressure (a pressure lower than the atmospheric pressure) generated in an intake pipe of an internal combustion engine is introduced into the evaporative fuel processing system to reduce the pressure in the evaporative fuel processing system, and the abnormality in the evaporative fuel processing system is determined according to the pressure in this system after the above pressure reduction. The evaporative fuel processing system includes a fuel tank, a canister for temporarily storing evaporative fuel generated in the fuel tank, and a charging passage for connecting the fuel tank and the canister.
According to the above abnormality detecting device, a leak in the fuel tank or the canister can be detected. However, the failure of an on-off valve provided in the charging passage cannot be detected.
It is accordingly an object of the present invention to provide an abnormality detecting device for an evaporative fuel processing system, which can detect the failure of the on-off valve provided in the charging passage for connecting the fuel tank and the canister.
In order to attain the above object, the present invention provides an abnormality detecting device for an evaporative fuel processing system. The evaporative fuel processing system includes a fuel tank (9), a canister (33) for trapping evaporative fuel generated in the fuel tank (9), a charging passage (31) for connecting the fuel tank (9) and the canister (33), a tank pressure regulating valve (35) provided in the charging passage (31), a bypass passage (31a) bypassing the tank pressure regulating valve (35), a bypass valve (36) provided in the bypass passage (31a), and a pressure sensor (15) provided in the fuel tank (9) or in the charging passage (31) at a position between the tank pressure regulating valve (35) and the fuel tank (9). The abnormality detecting device includes pressure reducing means and diagnosing means. The pressure reducing means reduces a pressure in the canister (33) to a pressure which is lower than the atmospheric pressure in the condition where a valve closing command signal for the bypass valve (36) is output. The diagnosing means determines that the tank pressure regulating valve (35) or the bypass valve (36) is abnormal when the pressure detected by the pressure sensor (15) becomes equal to or less than a predetermined threshold (the atmospheric pressure PAxe2x80x94DBPSOPN) during execution of the pressure reduction by the pressure reducing means.
With this configuration, the pressure in the canister is reduced in the condition where the valve closing command signal for the bypass valve is output, and when the pressure detected by the pressure sensor becomes equal to or less than the predetermined threshold during this pressure reduction, it is determined that the tank pressure regulating valve or the bypass valve is abnormal. If the bypass valve is normally closed in the condition where the valve closing command signal for the bypass valve is output, and the tank pressure regulating valve is normal, the pressure reduction in the canister has no influence on the pressure sensor output. In other words, if the pressure detected by the pressure sensor becomes equal to or less than the predetermined threshold during the pressure reduction in the canister, the tank pressure regulating valve or the bypass valve remains open. Accordingly, when the pressure detected by the pressure sensor becomes equal to or less than the predetermined threshold during the pressure reduction in the canister, it can be determined that the tank pressure regulating valve or the bypass valve is abnormal.
Preferably, the tank pressure regulating valve (35) includes a positive-pressure valve opened when the pressure in the fuel tank (9) is higher than the atmospheric pressure by a first predetermined pressure or more, and a negative-pressure valve opened when the pressure in the fuel tank (9) is lower than the pressure in the canister (33) by a second predetermined pressure or more. The diagnosing means preferably determines that the bypass valve (36) has failed or that the tank pressure regulating valve (35) has been improperly mounted, when the pressure (PTANK) detected by the pressure sensor (15) becomes equal to or less than the predetermined threshold (PAxe2x80x94DPBSOPN) during execution of the pressure reduction by the pressure reducing means.
With this configuration, in the case where the tank pressure regulating valve is a two-way valve including a positive-pressure valve and a negative-pressure valve, it is determined that the bypass valve has failed or that the tank pressure regulating valve has been improperly mounted, when the pressure detected by the pressure sensor becomes equal to or less than the predetermined threshold during the pressure reduction in the canister. That is, if a first port of the tank pressure regulating valve to be connected to the fuel tank is improperly connected to the canister, and a second port of the tank pressure regulating valve to be connected to the canister is improperly connected to the fuel tank, the negative-pressure valve opens due to the pressure reduction in the canister, resulting in a reduction in the pressure sensor output. Accordingly, when the pressure sensor output becomes equal to or less than the predetermined threshold during the pressure reduction in the canister, it can be determined that the tank pressure regulating valve has been improperly mounted or that the bypass valve has failed.
Preferably, the diagnosing means executes the determination when a predetermined waiting period (TSDEC1) has elapsed from the time of starting the pressure reduction by the pressure reducing means.
Preferably, the predetermined threshold is set to a value which is lower than the atmospheric pressure by a predetermined determination pressure.
Preferably, the diagnosing means determines that the tank pressure regulating valve (35) or the bypass valve (36) is abnormal, when the condition where the pressure (PTANK) detected by the pressure sensor (15) is less than or equal to the predetermined threshold (PAxe2x80x94DPBSOPN) continues for a predetermined determination period (CBPSCHK).
The present invention further provides an abnormality detecting device for an evaporative fuel processing system. The evaporative fuel processing system includes a fuel tank (9), a canister (33) for trapping evaporative fuel generated in the fuel tank (9), a charging passage (31) for connecting the fuel tank (9) and the canister (33), an on-off valve (36) provided in the charging passage (31) for opening and closing the charging passage (31), and a pressure sensor (15) provided in the fuel tank (9) or in the charging passage (31) at a position between the on-off valve (36) and the fuel tank (9). The abnormality detecting device includes pressure reducing means and diagnosing means. The pressure reducing means reduces a pressure in the canister (33) to a pressure which is lower than the atmospheric pressure in the condition where a valve closing command signal for the on-off valve (36) is output. The diagnosing means determines that the on-off valve (36) has failed, when the pressure (PTANK) detected by the pressure sensor (15) becomes equal to or less than a predetermined threshold (PAxe2x80x94DPBSOPN) during execution of the pressure reduction by the pressure reducing means.
With this configuration, the pressure in the canister is reduced in the condition where the valve closing command signal for the on-off valve is output, and when the pressure detected by the pressure sensor becomes equal to or less than the predetermined threshold during this pressure reduction, it is determined that the on-off valve has failed. If the on-off valve is normally closed in the condition where the valve closing command signal for the on-off valve is output, the pressure reduction in the canister has no influence on the pressure sensor output. In other words, if the pressure detected by the pressure sensor becomes equal to or less than the predetermined threshold during the pressure reduction in the canister, it is determined that a valve opening failure of the on-off valve has occurred such that the on-off valve is not closed in spite of supplying the valve closing command signal to the on-off valve. Accordingly, such a valve opening failure of the on-off valve can be detected.